Featured Research

from universities, journals, and other organizations

Superstorm Sandy shook the U.S., literally

Date:

April 18, 2013

Source:

University of Utah

Summary:

When superstorm Sandy turned and took aim at New York City and Long Island last October, ocean waves hitting each other and the shore rattled the seafloor and much of the United States – shaking detected by seismometers across the country, researchers found.

Share This

This map, taken from a University of Utah video, shows colored dots to represent the locations of portable seismometers in the Earthscope array, which is funded by the National Science Foundation. Most are now located in the eastern part of the United States. Blue-green dots indicate low seismic activity, while yellow-orange-red dots indicate stronger seismic activity. The map shows that when superstorm Sandy turned west-northwest toward Long Island, New York City and New Jersey on Oct. 29, 2012, the seismometers “lit up” because of ground shaking by certain ocean waves imparting energy to the seafloor.

When superstorm Sandy turned and took aim at New York City and Long Island last October, ocean waves hitting each other and the shore rattled the seafloor and much of the United States -- shaking detected by seismometers across the country, University of Utah researchers found.

Related Articles

"We detected seismic waves created by the oceans waves both hitting the East Coast and smashing into each other," with the most intense seismic activity recorded when Sandy turned toward Long Island, New York and New Jersey, says Keith Koper, director of the University of Utah Seismograph Stations.

"We were able to track the hurricane by looking at the 'microseisms' [relatively small seismic waves] generated by Sandy," says Oner Sufri, a University of Utah geology and geophysics doctoral student and first author of the study with Koper. "As the storm turned west-northwest, the seismometers lit up."

Sufri was scheduled to present the preliminary, unpublished findings in Salt Lake City Thursday, April 18 during the Seismological Society of America's annual meeting.

There is no magnitude scale for the microseisms generated by Sandy, but Koper says they range from roughly 2 to 3 on a quake magnitude scale. The conversion is difficult because earthquakes pack a quick punch, while storms unleash their energy for many hours.

The shaking was caused partly by waves hitting the East Coast, but much more by waves colliding with other waves in the ocean, setting up "standing waves" that reach the seafloor and transmit energy to it, Sufri and Koper say.

While many people may not realize it, earthquakes are not the only events that generate seismic waves. So do mining and mine collapses; storm winds, waves and tornadoes; traffic, construction and other urban activities; and meteors hitting Earth.

"They are not earthquakes; they are seismic waves," says Koper, a seismologist and associate professor of geology and geophysics. "Seismic waves can be created by a range of causes. … We have beautiful seismic records of the meteor that hit Russia. That's not an earthquake, but it created ground motion."

While Sandy's seismicity may be news to many, Koper says microseisms just as strong were detected before and after the superstorm from North Pacific and North Atlantic storms that never hit land but created "serious ocean wave action."

Koper adds: "Hurricane Katrina in 2005 was recorded by a seismic array in California, and they could track the path of the storm remotely using seismometers."

In a related study set for presentation on Friday at the seismology meeting, Koper and geophysics undergraduate student YeouHui Wong found preliminary evidence that seismometers near Utah's Great Salt Lake are picking up seismic waves generated either by waves or winds on the lake.

Koper says researchers wonder if microseisms from storms and other causes might trigger tiny but real earthquakes, but "that hasn't been investigated yet," he says.

Earthscope Picks up Seismic Waves from Ocean Wave Collisions

The microseisms generated by Sandy were detected by Earthscope, a National Science Foundation-funded array of about 500 portable seismometers that were first placed in California in 2004 and have been leapfrogging eastward so that most now are located east of line running from Minnesota to east Texas, and west of a line from Lake Erie to Florida. Some remain scattered across the Midwest and West, with a heavier concentration in the Pacific Northwest.

Earthscope's purpose is to use seismic waves from quakes and other sources to make images of Earth's crust and upper mantle beneath North America -- similar to how X-rays are used to make CT scans of the human body. To do it accurately, scientists must understand all sources of seismic waves.

Sufri says the new study included Earthscope data from Oct. 18 to Nov. 3, 2012, "which coincides with the passage of Hurricane Sandy, and we tried to understand microseisms that were generated."

Sandy caused a damaging storm surge due to its size -- almost 1,100 miles in diameter for tropical-storm-force winds -- more than its intensity, which was 3 when it hit Cuba and 2 off the Northeast coast.

"The energy generated by Sandy is going to be used to image the crust and upper mantle under North America," says Koper, noting that Earthscope uses years of seismic data to construct images. "We are using seismic waves created by ocean waves to make images of the continent."

Normal ocean waves "decay with depth very quickly," says Koper. But when Sandy turned, there was a sudden increase in waves hitting waves to create "standing waves" like those created when you throw two pebbles in a pond and the ripples intersect. "Pressure generated by standing waves remains significant at the seafloor," he says.

"When Sandy made that turn to the northwest, although wind speeds didn't get dramatically bigger, the seismic energy that was created got tremendously bigger because the ocean's standing waves were larger from the wave-wave interaction," he adds.

Not only did the seismic waves become more energetic, "but the periods got longer so, in a sense, the sound of those seismic waves got deeper -- less treble, more bass -- as the storm turned," Koper says.

Seismic Tracking of Hurricanes

Seismologists can track Sandy and other big storms because seismometers detect three components of motion: one vertical and two horizontal. If most of the energy on a seismometer is detected with a north-south motion, it means the source of the energy is north or south of the device.

"If you have enough seismometers, you can get enough data to get arrows to point at the source," Koper says.

He says the seismologists didn't track Sandy in real time, but the seismographic data of the storm suggests it might be possible to help track storms in the future using their seismicity.

Sufri speculates that seismic tracking of storms might allow observations that satellites can miss, and perhaps could help researchers "understand how climate is changing and how it is affecting our oceans -- are we seeing more intense storms and increasing numbers of storms?"

Koper says the Sandy study "is exploratory science where we are trying to learn fundamental things about how the atmosphere, oceans and solid Earth interact."

Featured Research

Mar. 31, 2015  As the five-year anniversary of the explosion of the Deepwater Horizon oil rig approaches, a new report looks at how twenty species of wildlife are faring in the aftermath of the ... full story

Mar. 31, 2015  Scientists have discovered why the first buds of spring come increasingly earlier as the climate changes. As the climate changes the sweet spot for seeds comes earlier in the year, so first flowers ... full story

Mar. 31, 2015  In the 1990s the discovery of the oldest human made and completely preserved wooden hunting weapons made the Paleolithic excavation site in Schoningen internationally renowned. Contained within the ... full story

Mar. 31, 2015  The adverse health effects caused by fine particles have been known for some time. In addition, ultrafine particles appear to play a significant role in cardiac function -- even if an individual is ... full story

Mar. 30, 2015  Researchers have identified a new source of methane for gas hydrates -- ice-like substances found in sediment that trap methane within the crystal structure of frozen water -- in the Arctic Ocean. ... full story

Mar. 30, 2015  A new study reports that marine ecosystems can take thousands, rather than hundreds, of years to recover from climate-related upheavals. The study's authors analyzed thousands of invertebrate fossils ... full story

Mar. 30, 2015  By studying the morphology and physiology of plants with tiny conical "hairs" or microfibers on the surface of their leaves, such as tomatoes, balsam pears and the flowers Berkheya purpea and Lychnis ... full story

Mar. 30, 2015  The 2000-2003 drought in the American southwest triggered a widespread die-off of forests around the region. A team of scientists developed a new modeling tool to explain how and where trembling ... full story

Mar. 30, 2015  A new study has confirmed the existence of a positive feedback operating in climate change whereby warming itself may amplify a rise in greenhouse gases resulting in additional ... full story

Related Stories

Dec. 5, 2013  Geoscientists estimate that the New Jersey shore will likely experience a sea-level rise of about 1.5 feet by 2050 and of about 3.5 feet by 2100 -- 11 to 15 inches higher than the average for ... full story

June 24, 2013  Researchers have released results of a major survey exploring resilience of people and neighborhoods directly affected by Superstorm Sandy. The study reveals the importance of social factors such as ... full story

Mar. 5, 2013  Researchers have shown that the severe loss of summertime Arctic sea ice – attributed to greenhouse warming – appears to increase the frequency of atmospheric blocking events like the one that ... full story

Nov. 8, 2012  On October 29, 2012, lives were changed forever along the shores of New Jersey, New York, Connecticut, and in the two dozen United States affected by what meteorologists are calling Superstorm Sandy. ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.